Digital PreDistortion (DPD) is a digital technique mainly known for improving the linearity of power amplifiers. Power amplifiers operate with better or more energy efficiency when a certain degree of nonlinearity is allowed—typically compression of the input signal (i.e. a smaller gain at higher amplitudes is allowed). The nonlinear input-output relationship changes the harmonic content of the signal. This causes, e.g., harmonic distortions (i.e. overtones that are multiples of the input signal frequencies) or inter-modulation distortions (i.e. additional signal components at frequencies that are the sum and difference of the frequencies of the original input signal components and at frequencies that are multiples of those sum and difference frequencies). These distortions may introduce interference in both adjacent and distant signal channels. With each new communication standard, the requirements regarding the maximum allowed interference in other radio channels are getting stricter.
Similarly, digital to analog converters (DAC) are also affected by nonlinearity (although the nonlinearity may be reduced as described above)—for example if the digital to analog converters are designed for low power consumption. In addition to the inherent nonlinearity of the digital to analog converter itself (e.g. due to the use of nonlinear elements such as transistors, see above), there are other effects that translate into nonlinear behavior. For example, a non-ideal power supply, an associated network, component mismatches or clock distribution skew.
DPD may be used to mitigate the digital to analog converter nonlinearity. For proper mitigation of the digital to analog converter nonlinearity, a trained DPD (e.g. a DPD algorithm) is needed.
Hence, there may be a desire for improved DPD training architectures.